Testing subterranean formations



March 20, 1951 B. w. SEWELL 2,545,975

TESTING SUBTERVRANEAVN FORMATIONS Filed Aug. 6, 1947 2 Sheets-Sheet 1 TEST PIPE TESTPIDE f i DRILL I E 2 PIPE f 3 TEST AREA 1 II-+551 1 AREA FLU-I'D filliuLATloN O11 TEST OtLTS 1 16-4 QJeryamta Saw-ell {Sm/armor abbom March 20, 1951 B. w. SEWELL 2,545,975

TESTING SUBTERRANEAN FORMATIONS 1 Filed Aug. 6, 1947 2 Sheets-Sheet 2 KELLY WnzE V15 PQQDUQED FLUID OUTLET berzjczmtrz CJT Secd'ell Srzvsabor 33 .5%. Cltborrmc s Patented Mar. 20, 1951 2,545,975 TESTING SUBTERRANEAN FORMATIONS Benjamin W. Sewell, Tulsa, Okla., assignor to Standard Oil Development Company, a corporation of Delaware Application August 6, 1947, Serial No. 766,834

4 Claims.

The present invention is directed to a method for testing formations traversed by a bore hole.

In the drilling of an oil well it is important to know whether or not a given formation penetrated contains oil in productive quantities and is susceptible to ordinary methods of production. It has been customary to determine this by a drillstem test. This operation is performed in many ways but it involves in essence the sealing off of the formation to be tested from the rest of the hole and the opening of, this formation to substantially atmospheric pressure. Ordinarily the drill stem, having been brought to the surface usually after drilling a rat hole into the formation to be tested, has aflixed to its lower end a valve mechanism below which is a packer and the assembly is lowered into the hole until the packer is seated on the rat hole. Then the valve is opened from the surface exposing the formation penetrated by the rat hole to the empty drill stem whereupon any fluid contained in the formation under pressure will run into the drill stem. Then the valve is closed and the assembly is brought to the surface and the fluid content of the drill stem is examined.

As areas have been encountered in which a plurality of potential producing horizons are penetrated, the number of drill stem tests required during drilling operation has increased. This has led to a need fora more simple inexpensive method for conducting these tests.

An important consideration, however, in connection with drill stem tests as they have been conducted in the past has been the fact that during a drill stem test circulation of the drilling fluid is stopped. This is a cause for considerable concern because these stoppages are often for extended periods and in some cases have led to the freezing of the drill stem by virtue of the settling of cuttings and heavier constituents from the drilling fluid to the bottom of the holearound the drill stem.

The principal object of. the present invention is the provision of a simplemethod for conducting a drill stem test which'does not involve stopping the circulation of the..:d l illing fluid.

An additional object of the present invention is the provision of a method for performing a drill stem test which involves fewer manipulative steps than those heretofore in use.

Further objects and advantages of the present invention will appear from. the following detailed description of the accompanying. drawing in which, A

Figure 1 is a vertical section through a borehole with the elements required for the performance of the present invention in its simplest embodiment in operative position;

Figure 2 is a view of the well head equipment partly in section when a rat hole is being drilled;

Figure 3 is a similar view of the well head equipment employed during the drill stem test;

Figure 4 is a view corresponding to Figure 1 showing an alternative embodiment of apparatus suitable for the practice of the present invention.

Referring to the drawing in detail, numeral I designates a bore hole in the earth in which is arranged a drill stem 2. This drill stem is provided with a conventional bit 3, of the type used for coring operations, having an enlarged cen tral passage 4.

Let it be assumed that the bore hole has been drilled to the point indicated and it is desired to run a drill stem test. A smaller drill stem, having substantially the diameter of pipe 5, is lowered down through the main drill stem and through the opening 4. This smaller drill stem carries a smaller bit with which is drilled a rat hole 6, mud circulation being conducted during this operation. The smaller drill stem is then withdrawn and the test pipe 5, having at its lower end a perforated nipple 1 and a packer 8 arranged above the perforated nipple is lowered into the drill stem. The packer may be any of the commonly known packers and its particular construction forms no part of the present invention. It will ordinarily be a packer which is expanded by setting the lower end of the test tube on the bottom and exerting pressure upon it. With the packer set as indicated swabbing is begun in the test tube 5. All during this period'circulation of drilling fluid in the bore hole is continued except for the relatively brief interruptions required for the insertion of the narrow drill stem and the substitution of the test tube pipe for the drill stem. Swabbing may be conducted as long as desired until the operator is satisfied that the test is completed.

One of the foregoing steps can be omitted by usin the smaller drill pipe referred to as the test pipe. In other words the lower end of the smaller drill pipe may be perforated and provided with a packer which is notset until the rat hole is drilled.

Such an arrangement is shown in Figure 4 in which the test pipe 5 carries at its lower end a drill bit 9. In this case, there is secured to the test pipe an ordinary conical packer l0 which is spaced from the drill bit a distance corresponding to the desired rat hole length. Thus a rat hole is drilled by the test pipe and, when the rat hole reaches the predetermined depth, continued pressure on the test pipe seats the packer on the rat hole.

It will be understood that a continuous recording pressure gauge may be arranged in the nipple 7. Also it will be generally preferred to maintain the test pipe empty until the testing operation begins. This can easily be provided for by placing a frangible disc in the test pipe at about the location of the packer which forms a seal. Then in order to begin the test a godevil or a metal ball is dropped down through the test pipe to shatter the frangible disc. This expedient is old in testing equipment of this type.

In Figure 2 is shown the well head equipment when a rat hole is being drilled with a separate drill stem. In this case, the regulation drill pipe 2 is provided at its upper end with a cap I I in which is a packing gland l2 of the conventional type used in lubricators. Drilling mud is introduced into the upper end of the regulation drill pipe through line i3, passes down through the drill pipe and up through the annular space M between the drill pipe and the wall of the borehole. During the drilling of the rat hole circulation may, if desired, be maintained in the inner drill stem in the usual way by connecting a mud line to the kelly [5.

In Figure 3 the test pipe 5 is shown passing through the packing gland l2. The test pipe in turn c'arries'at its upper end a packing gland or lubricator 16, through which passes a wire line i'L'carrying at its lower end a swab 18 of any conventional design. When the test is started the swab is lowered down into the test pipe and drawn upwardly in the conventional manner raising any formation fluid to outlet. pipe [9.

It will be apparent that many variations of the simple embodiment illustrated and described above can be devised without departing from the scope of the present invention. The important featureis that the testing equipment is passed through the conventional drill stem and circulation of drilling fluid is maintained during the testing operation.

The nature and objects of present invention having been thus described and illustrated what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A method for testing a subterranean formation for its fluid content which comprises drilling a borehole substantially to said formation with a drillstem having a drill bit with an enlarged central opening, inserting into said drill stem a smaller drill stem capable of passing through said opening, both of said drill stems extending to the earths surface, drilling a rat hole into said formation with said smaller drill stem while maintaining circulation of drilling fluid in said larger drill stem and in the bore hole, sealing off said rat hole from the bore hole while continuing said circulation of drilling fluid in said bore hole, ex-

posing the sealed off portion of said rat hole to reduced pressure and collecting through said smaller drill stem fluid secreted by the formation exposed by said rat hole, while continuing the circulation of drilling fluid in said bore hole and in said first named drill stem.

2. A method for testing a subterranean formation for its. fluid content which comprises drilling a bore hole substantially to said formation with a drill stem having a drill bit with an enlarged central opening, inserting into said drill stem a smaller drill stem having a perforated lower end and carrying a drill bit at its lower end capable of passing through said central opening, both of said drill stems extending to the earths surface, drilling a rat hole into said formation with said smaller drill stem while maintaining circulation of drilling fluid in said first drill stem and in the bore hole, sealing off said rat hole from the bore hole while continuing circulation of drilling fluid in said bore hole, exposing the sealed-off portion of said rat hole to a reduced pressure and collecting through said smaller drill stem fluid secreted by the formation exposed by said rat hole as a result of saidreduction in pressure, while continuing the circulation of drilling fluid throughsaid bore hole and said first named drill stem.

3. A method accordingto claim 2 in which said smaller drill stem is maintained empty and with its interior at atmospheric pressure .until said rat hole is sealed off and is then placed in fluid communication with theformation exposed by said rat hole.

4. Apparatus fortesting a subterranean formation for its fluid content which comprises a drill stem, a drillbit attached to the lower end thereof, said drill bit having an enlarged central opening, a second smaller drill stemadapted to fit within said first drillstem and to form a substantial annular space between the two drill stems, both of said drill stems extending to the earths surface said smaller drill stem having perforations adjacent its lower end, a second drill bit attached to said smaller drill stem and adapted to pass through said enlarged central opening in said first drill bit, and a packer carried by said smaller drill stem above said perforations and adapted to pass through said enlarged central opening in said first drill bit.

BENJAMIN W. SEWELL.

REFERENCES CITED The following references are of recordin the file of this patent:-

UNITED STATES PATENTS Parks Apr. 12,1938 

